A critical review on the electrosorption of organic compounds in aqueous effluent - Influencing factors and engineering considerations

Electron exchange capacity of dissolved natural organic matter: further method development and interpretation using square wave voltammetry in dimethyl sulfoxide

Most measurements of the electron exchange capacity (EEC) of natural organic matter (NOM) have been done in water using mediated chronoamperometry (MCA), which gives precise results that are believed to be representative of the samples' current redox condition, but the broader significance of these EECs is less clear. In a recent study, we described a novel but complementary electrochemical approach to quantify EECs of 10 pyrogenic dissolved organic matter (pyDOM) and 6 standard/reference natural organic matter (NOM) materials without mediation using square-wave voltammetry (SWV) in dimethyl sulfoxide (DMSO). Comparison of the results obtained by MCA and SWV showed that SWV in DMSO gave larger EECs than MCA, by several-fold for NOM and 1-2 orders of magnitude for pyDOM. In this study, we describe an improved protocol for calibration of the SWV/DMSO method, which largely eliminates the difference in EECs from SWV and MCA for the standard/reference NOM samples. The results show that values obtained via the SWV method depend on the specific redox standards used for calibration (i.e., calibrant model compounds), with slopes that span 1.5 orders of magnitude due to variations in current response factors. For pyDOM, the higher values of EEC obtained by SWV were further verified and rationalized. Like the calibrant model compounds, it is proposed that the relatively large EECs for some pyDOM samples from high-temperature chars reflect a combination of hydrodynamic influences in our electrochemical cell, primarily related to electrode surface area to volume ratio and pyDOM size. A detailed explanation of the calibration method, choice of working electrode, DOM sorption effects, and cosolvent effects are discussed. The results obtained with this method suggest that the capacity of NOM for donating, accepting, and storing elections is an operationally defined property, the significance of which will depend on application, e.g., to carbon, metal, or nutrient cycling, pollutant attenuation, etc.

Influence of interelectrode distances in electrocoagulation: is there any possibility and advantages to operate at micro-distances with low-conductivity effluents?

It has been proposed for the first time to investigate the possibility to implement micro-inter-electrode distances in electrocoagulation (EC) in order to improve both the treatment and energy efficiencies compared to conventional EC cells with centimetric distances. The study has been performed in a microfluidic monopolar flow-by filter-press cell for the treatment of simulated and real low-conductivity (0.5-1 mS cm-1) laundry wastewaters. The influences of interelectrode distance (delec) (100-10,000 μm), applied current density (japp) (10-200 mA cm-2), and types of anode materials (iron, aluminium and stainless steel) have been studied. The removal of representative organic pollutant (i.e., paracetamol at 15 mg L-1) as well as of total organic carbon (TOC) content (312 mg-C L-1) from actual wastewater was noticed, including at micro-distances. Optimal treatment capacities were obtained with delec of 0.5 mm (57% TOC removed), 3 mm (58% TOC removed) and 10 mm (41% TOC removed) and with japp of 70 mA cm-2, 40 mA cm-2 and 20 mA cm-2 respectively, using stainless steel anode. It led to reduced energy requirement at micro-distances (16 kWh g-TOC-1 at 500 μm) compared to millimetric gap (19 kWh g-TOC-1 at 3 mm, 40 kWh g-TOC-1 at 10 mm). Contrastingly, more sludge was generated with micrometric distance (172 g-sludge g-TOC-1 at 500 μm) compared to larger gaps (95 g-sludge g-TOC-1 at 3 mm, 87 g-sludge g-TOC-1 at 10 mm) due to higher optimal japp at low distances. The efficiency was maximal with an aluminium electrode, but this anode remained inapplicable with micro-distances using the current reactor design, given the high sludge production between the cathode and anode.

Electrochemical Sensing Strategies for Synthetic Orange Dyes

This review explores electrochemical sensing strategies for synthetic orange dyes, addressing the growing need for sensitive and selective detection methods in various industries. We examine the fundamental principles underlying the electrochemical detection of these compounds, focusing on their redox behavior and interaction with electrode surfaces. The review covers a range of sensor designs, from unmodified electrodes to advanced nanomaterial-based platforms. Chemically modified electrodes incorporating polymers and molecularly imprinted polymers are discussed for their enhanced selectivity. Particular attention is given to nanomaterial-based sensors, including those utilizing carbon nanotubes, graphene derivatives, and metal nanoparticles, which have demonstrated exceptional sensitivity and wide linear ranges. The potential of biological-based approaches, such as DNA interaction sensors and immunosensors, is also evaluated. Current challenges in the field are addressed, including matrix effects in complex samples and long-term stability issues. Emerging trends are highlighted, including the development of multi-modal sensing platforms and the integration of artificial intelligence for data analysis. The review concludes by discussing the commercial potential of these sensors in food safety, environmental monitoring, and smart packaging applications, emphasizing their importance in ensuring the safe use of synthetic orange dyes across industries.

Bio-based composite from chitosan waste and clay for effective removal of Congo red dye from contaminated water: Experimental studies and theoretical insights

Water pollution due to dyes in the textile industry is a serious environmental problem. During the finishing stage, Congo red (CR) dye, water-soluble, is released into wastewater, polluting the water body. This study explores the effectiveness of utilizing a composite composed of Safi raw clay and chitosan to remove an anionic dye from synthetic wastewater. The chitosan was extracted from crab shells. Its removal performance was compared to that of natural clay. Both the composite and raw clay were used to remove target pollutant. The effects of the chitosan load in the composite, size particles, initial dye concentration, contact time, pH, and temperature on the dye's elimination were tested in batch modes. The composite with 30% (w/w) of chitosan exhibited the highest dye removal. At pH 2, an adsorption capacity of 84.74 mg/g was achieved, indicating that the grafting of the polymer onto clay surface enhances its efficacity and stability in acidic environments. This finding was supported by characterization data obtained from X-ray diffraction (XRD), scanning electron microscopy (SEM), dispersive X-ray spectroscopy (EDX), and Fourier transform infrared (FT-IR) analyses. Under optimized conditions of 20 mg dose, pH 2, 30 min of reaction time, and 20 mg/L of dye concentration, about 92% of dye removal was achieved. The Langmuir isotherm model represents dye adsorption by the composite, while dye removal was controlled by pseudo-second-order model. Thermodynamic data of the adsorption (ΔH = +8.82 kJ/mol; ΔG <0) suggested that the dye adsorption was spontaneous and endothermic. The findings provide insights into the dye elimination by the adsorbent, indicating that the removal occurred via attractive colombic forces, as confirmed by density functional theory (DFT) analysis. Overall, the composite of natural clays and chitosan waste is a promising and innovative adsorbent for treating wastewater containing recalcitrant dyes.

Optimization of preparation conditions of a novel low-cost natural bio-sorbent from olive pomace and column adsorption processes on the removal of phenolic compounds from olive oil mill wastewater

Olive oil mill wastewater (OMWW) poses an undeniable environmental problem due to its high organic loads and phenolic compound (PC) content. This study determined the optimal conditions for preparing a new bio-sorbent from olive pomace (OP) and the adsorptive treatment of OMWW by this bio-sorbent. The activation reaction was performed with hydrogen peroxide. The results of the combination effect optimization of the three preparation variables, the activation temperature (°C) X₁, the activation time (min) X₂, and the impregnation ratio X₃, are presented by the response surface methodology (RSM). The maximum adsorption capacity was obtained at an activation time of 240 min, a temperature of 80 °C, and a ratio equal to 6.2:1. The bio-sorbent was characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffractometer (XRD). The adsorption process performance of this bio-sorbent was examined in batch (phenol solution) and fixed-bed columns (real effluent of OMWW). An adsorption capacity of 789.28 mg g^-1 and 643.92 mg g^-1 has been achieved for 4000 mg L^-1 concentration of PCs, respectively, for batch and fixed-bed column essays. The adsorption isotherm and kinetics were consistent with the Langmuir and pseudo-second-order models. Therefore, the Thomas model best fits the fixed-bed column experimental data. The bio-sorbent gave a high desorption percentage of PCs, which was above 60% using HCl (0.1M).

Emerging electrochemical techniques for identifying and removing micro/nanoplastics in urban waters

The ubiquitous micro/nanoplastics (MPs/NPs) in urban waters are priority pollutants due to their toxic effects on living organisms. Currently, great efforts have been made to realize a plastic-free urban water system, and the identification and removal of MPs/NPs are two primary issues. Among diverse methods, emerging electrochemical techniques have gained growing interests owing to their facile implementation, high efficiency, eco-compatibility, onsite operation, etc. Herein, recent progress in the electrochemical identification and removal of MPs/NPs in urban waters are comprehensively reviewed. The electrochemical sensing of MPs/NPs and their released pollutants (e.g., bisphenol A (BPA)) has been analyzed, and the sensing principles and the featured electrochemical devices/electrodes are examined. Afterwards, recent applications of electrochemical methods (i.e., electrocoagulation, electroadsorption, electrokinetic separation and electrochemical degradation) in MPs/NPs removal are discussed in detail. The influences of critical parameters (e.g., plastics' property, current density and electrolyte) in the electrochemical identification and removal of MPs/NPs are also analyzed. Finally, the current challenges and prospects in electrochemical sensing and removal of MPs/NPs in urban waters are elaborated. This review would advance efficient electrochemical technologies for future MPs/NPs pollutions management in urban waters.

Recent advances in electrocatalytic membrane for the removal of micropollutants from water and wastewater

The increasing occurrence of micropollutants in water and wastewater threatens human health and ecological security. Electrocatalytic membrane (EM), a new hybrid water treatment platform that integrates membrane separation with electrochemical technologies, has attracted extensive attention in the removal of micropollutants from water and wastewater in the past decade. Here, we systematically review the recent advances of EM for micropollutant removal from water and wastewater. The mechanisms of the EM for micropollutant removal are first introduced. Afterwards, the related membrane materials and operating conditions of the EM are summarized and analyzed. Lastly, the challenges and future prospects of the EM in research and applications are also discussed, aiming at a more efficient removal of micropollutants from water and wastewater.